In many contexts, industry uses various types of machine tools for processing and manufacturing various parts. This involves the need to be able to monitor the status of such machines in order, for example, to be able to do repairs and adjustments in time to avoid stoppages or bad precision of parts being manufactured. The objective is to be able to detect changes quickly and to be able to rectify them before major and expensive defects develop.
A conventional method for testing a machine is to make representative parts and then check their dimensions in order to assess the machine's performance. Disadvantages observed in this respect include the need to use tools and test pieces and difficulty in comparing results from different tests. Using standardised test pieces certainly facilitates comparisons but still requires test pieces and tools.
Another method comprises monitoring the machine's rigidity in different directions by applying a suitable force by means of a hydraulic cylinder and measuring the resulting deflection by means, for example, of a micrometer. A disadvantage of this method is that it is time-consuming and measurement cannot be done with the machine in operation.
A further known practice comprises the use of a special instrument, a so-called “ball bar”, fitted between workpiece holders and tool holders, to test the machine's ability to perform a circular movement. Measuring equipment in the instrument is used to record any deviations from a circle. Various such tests can be carried out at different times and compared to provide information on various characteristics of the machine, such as circularity, servo response, rectilinearity, play etc. Tests can also be done at various feed rates, in various feed directions and using bars of various lengths, and placing the workpiece holder at various different points. There nevertheless remains the disadvantage of it not being easy to gain a proper assessment of the machine's characteristics under load.
US 2002/0189379 A1 solves this problem by applying a predetermined static force between the first and second elements during mutual displacement between them, and simultaneously measuring the resulting deformation. This makes it possible to carry out machine testing in much more production-like conditions than was previously possible. Analysis can be further refined by also varying the manner in which the displacement takes place, as regards both movement configuration and direction of movement, and also by varying the magnitude of the force applied.